Keywords
band gap, optical constant, thickness measurement, thorium oxide, spectroscopic ellipsometry, thoria, refractive index, DC-bias, sputtering, x-ray diffraction
Abstract
We use spectroscopic ellipsometry to determine the optical constants of seven thin-film ThO2 samples deposited by radio-frequency sputtering, thickness ranging between 24 and 578 nm, for the spectral range of 1.2 to 6.5. We used a hollow-cathode light source and vacuum monochromator to measure constants at 10.2 eV. None of the deposition parameters studied including DC-bias voltages successfully increased the n of (that is, densify) thoria films. The value of n at 3.0 eV is 1.86 ± 0.04. We find compelling evidence to conclude that the direct bad gap is at ~5.9 eV, clarifying the results of others, some of whom observed the absorption edge below 4 eV. the edge in the two thickest films is of a narrow feature (FWHM = 0.4 eV) with modest absorption (α~ 6µm-1, K~0.1). Absorption may go down briefly with increasing energy from 6.2 to 6.5 eV). But at 10.2 eV absorption is very high and index low as measured by variable angle reflectometry, α= 47.3 ± 5.5 µm-1 and K= 0.48 ± 0.05, and n= 0.87 ± 0.12.
Original Publication Citation
William R. Evans, Sarah C. Barton, Michael Clemens and David D. Allred, "Understanding DC-Bias Sputtered Thorium Oxide Thin Films Useful in EUV Optics [6317-37]," in: Advances In X-Ray/EUV Optics, Components, And Applications, edited by Ali M. Khounsary, and Christian Morawe, Proceedings of SPIE, 6317, 631711-1 to 8 (26). [http://spiedigitallibrary.org/proceedings/resource/2/psisdg/6317/1/631711_1?isAuthorized=no][http://dx.doi.org/1.1117/12.687499].
BYU ScholarsArchive Citation
Evans, William R.; Barton, Sarah C.; Clemens, Michael; and Allred, David D., "Understanding DC-Bias Sputtered Thorium Oxide Thin Films Useful in EUV Optics" (2006). Faculty Publications. 990.
https://scholarsarchive.byu.edu/facpub/990
Document Type
Peer-Reviewed Article
Publication Date
2006-08-13
Permanent URL
http://hdl.lib.byu.edu/1877/2919
Publisher
Society of Photo Optical Instrumentation Engineers (SPIE)
Language
English
College
Physical and Mathematical Sciences
Department
Physics and Astronomy
Copyright Status
© 2006 Society of Photo Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
Copyright Use Information
http://lib.byu.edu/about/copyright/
